x86/unwind: Make CONFIG_UNWINDER_ORC=y the default in kconfig for 64-bit

The ORC unwinder has been stable in testing so far.  Give it much wider
testing by making it the default in kconfig for x86_64.  It's not yet
supported for 32-bit, so leave frame pointers as the default there.
Suggested-by: NIngo Molnar <mingo@kernel.org>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/9b1237bbe7244ed9cdf8db2dcb1253e37e1c341e.1507924831.git.jpoimboe@redhat.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

arch/x86/Kconfig.debug

@@ -358,27 +358,13 @@ config PUNIT_ATOM_DEBUG
 
 choice
 	prompt "Choose kernel unwinder"
-	default UNWINDER_FRAME_POINTER
+	default UNWINDER_ORC if X86_64
+	default UNWINDER_FRAME_POINTER if X86_32
 	---help---
 	  This determines which method will be used for unwinding kernel stack
 	  traces for panics, oopses, bugs, warnings, perf, /proc/<pid>/stack,
 	  livepatch, lockdep, and more.
 
-config UNWINDER_FRAME_POINTER
-	bool "Frame pointer unwinder"
-	select FRAME_POINTER
-	---help---
-	  This option enables the frame pointer unwinder for unwinding kernel
-	  stack traces.
-
-	  The unwinder itself is fast and it uses less RAM than the ORC
-	  unwinder, but the kernel text size will grow by ~3% and the kernel's
-	  overall performance will degrade by roughly 5-10%.
-
-	  This option is recommended if you want to use the livepatch
-	  consistency model, as this is currently the only way to get a
-	  reliable stack trace (CONFIG_HAVE_RELIABLE_STACKTRACE).
-
 config UNWINDER_ORC
 	bool "ORC unwinder"
 	depends on X86_64
@@ -395,6 +381,21 @@ config UNWINDER_ORC
 	  Enabling this option will increase the kernel's runtime memory usage
 	  by roughly 2-4MB, depending on your kernel config.
 
+config UNWINDER_FRAME_POINTER
+	bool "Frame pointer unwinder"
+	select FRAME_POINTER
+	---help---
+	  This option enables the frame pointer unwinder for unwinding kernel
+	  stack traces.
+
+	  The unwinder itself is fast and it uses less RAM than the ORC
+	  unwinder, but the kernel text size will grow by ~3% and the kernel's
+	  overall performance will degrade by roughly 5-10%.
+
+	  This option is recommended if you want to use the livepatch
+	  consistency model, as this is currently the only way to get a
+	  reliable stack trace (CONFIG_HAVE_RELIABLE_STACKTRACE).
+
 config UNWINDER_GUESS
 	bool "Guess unwinder"
 	depends on EXPERT